1. Field of the Invention
The present invention relates to a decorative key sheet for pushbutton switches for use in an operating portion of an electronic instrument such as a mobile information terminal, a PDA, an AV instrument, various remote control units, or various keyboards.
2. Description of the Related Art
A reduction in size and thickness of electronic instruments such as mobile information terminals and PDAs is under way, and there is a demand for a thin type input component such as a key sheet for those instruments allowing realization of a reduction in thickness of electronic instruments. On the other hand, various decorations for an enhancement in design value are imparted to key sheets so as to achieve product differentiation thereof and to give a quality appearance thereto; among such decorations is a hairline pattern with a metallic luster. In this context, thin key sheets with a hairline pattern have been realized by the following techniques.
For example, by using the techniques as disclosed in JP 2002-008476 A and JP 2006-156333 A, which utilize a metal plate such as an aluminum plate or a stainless steel plate, it is possible to impart a fine asperity pattern to the surface of a metal plate, thereby realizing a key sheet of a hairline pattern with a metallic luster.
Further, as disclosed in JP 06-305063 A and JP 2005-111865 A, by providing a fine asperity hairline pattern on the surface of a resin sheet and covering the surface with a metal thin film layer, a metallic coating layer or the like, it is possible to realize a key sheet of a hairline pattern with a metallic luster.
Further, according to the techniques disclosed in JP 2003-109450 A and JP 2006-185699 A, a fine asperity hairline pattern is formed on the back surface of a transparent member, and a metal thin film layer, a metallic coating layer or the like is provided on the hairline pattern surface, whereby it is possible to realize a key sheet of a hairline pattern with a metallic luster.
However, while the techniques using a metal plate as disclosed in JP 2002-008476 A and JP 2006-156333 A provide high durability for the asperity pattern and make it possible to maintain the metallic luster, in the case of a component to be touched with the hand such as a key sheet, there is a fear of the operator being injured by the forward end portion or edge portion of the metal plate, so it is necessary to smoothen the forward end portion and edge portion by polishing, etching or the like or cover the forward end portion and edge portion with a polymer material. Thus, the production takes a lot of time and effort, resulting in a rather high cost.
In the resin surface decorating techniques as disclosed in JP 06-305063 A and JP 2005-111865 A, it is possible to achieve an improvement in terms of safety as compared with the techniques using a metal plate; however, the metal thin film layer, the metallic coating film layer or the like is subject to wear through touching with the hand; further, they are easily separated from the resin, so it is rather difficult to maintain the quality appearance. Further, covering the fine asperity surface with a metal thin film layer, a metallic coating film layer or the like results in the recessed portions of the pattern being filled up, which makes the hairline pattern rather inconspicuous, thus making it rather difficult to attain the desired design value.
In the techniques as disclosed in JP 2003-109450 A and JP 2006-185699 A, in which the back surface of a transparent member is decorated, it is possible to prevent wear and separation of the metal thin film layer, the metallic coating film layer or the like; however, it is rather difficult to visually recognize the fine asperity hairline pattern through the transparent member. When, in order to enhance the visibility, the surface of the transparent member is formed as a smooth surface, the surface of the transparent member becomes subject to staining through touching with the hand, etc., thereby impairing the quality appearance.